The adult mammalian central nervous system contains a population of immature, undifferentiated, multipotent cells, neural stem cells (NSCs) that may be called upon for repair in neurodegenerative and demyelinating diseases. NSCs may, in turn, give rise to oligodendrocyte progenitor cells (OPCs) and other myelinating cells, as well as neural and glial precursors. The capacity of NSCs to repair damage in the adult has been demonstrated in several experimental systems. However, in multiple sclerosis and its animal model experimental autoimmune encephalomyelitis (EAE) remyelination and neuro-regeneration do not occur to a sufficient extent. During the previous funding period we have examined the effects of inflammation on the multipotentiality of neural stem/progenitor cells in vivo and in vitro. We found that NSCs proliferate, start to differentiate, and migrate out of the subventricular zone during the acute phase of the disease. But as the disease progresses proliferation of the stem cells subsides. Furthermore, we have observed that during chronic EAE, microglia remain activated in the absence of inflammatory infiltrates. This situation is reminiscent of the chronic phase of multiple sclerosis, where neuro-degeneration and loss of brain parenchyma occur in the absence of gadolinium enhancing lesions on MRI. We will examine the hypothesis that chronically activated microglia are responsible, at least in part for the dysfunction in stem cell function. We will address this hypothesis in the following aims. Aim 1. Differential interaction of acutely versus chronically activated microglia with neural progenitor cells. Aim 2. How do NSCs modulate microglial activation in the SVZ. Aim 3. We will examine if reversal of chronic microglia activation will restore normal NSC functionality. These investigations will have an impact on our understanding of the pathogenesis of neuro-degeneration in multiple sclerosis and provide a model that may be used to target treatments for chronic disease.